The present invention relates to new delivery systems for cyclopropenes in which the cyclopropene, either free or encapsulated within a molecular encapsulation agent, is incorporated into packaging materials for agricultural produce and ornamental plants.
It is well known that ethylene can cause the premature death of plants or plant parts including, for example, flowers, leaves, fruits, and vegetables through binding with certain receptors in the plant. Ethylene is known to promote leaf yellowing and stunted growth as well as premature fruit, flower, and leaf drop. In addition, ethylene is also known to induce or accelerate the ripening of harvested fruits and vegetables. Because of these ethylene-induced problems, very active and intense research presently concerns the investigation of ways to prevent or reduce the deleterious effects of ethylene on plants. U.S. Pat. No. 5,518,988 discloses the use of cyclopropene and its derivatives, including methylcyclopropene, as effective blocking agents for ethylene binding. However, a major problem with these compounds is that they are typically unstable gases which present explosive hazards when compressed. U.S. Pat. No. 6,017,849 discloses a method of incorporating these gaseous compounds into a molecular encapsulation agent complex in order to stabilize their reactivity and thereby provide a convenient and safe means of storing, transporting and applying or delivering the active compounds to plants as a way to alleviate these problems. For the most active cyclopropene derivative disclosed in U.S. Pat. No. 5,518,988, 1-methylcyclopropene (xe2x80x9c1-MCPxe2x80x9d), the preferred molecular encapsulation agent is a cyclodextrin, with xcex1-cyclodextrin being the most preferred. The application or delivery of these active compounds to plants is accomplished by simply adding water to the molecular encapsulation agent complex. The complex is prepared according to the methods disclosed in U.S. Pat. No. 6,017,849 which provides the material in the form of a powder.
The powdered complex is usually added to water to release the 1-MCP into the atmosphere where plants or plant parts to be treated are stored, that is, a treatment container or room. Typical treatment concentrations are 0.1 to 1.0 ppm (vol/vol) in the atmosphere surrounding the plant or plant parts. In order to accomplish this release large amounts of water are required, at least ten times and preferably twenty times the weight of the 1-MCP/xcex1-cyclodextrin complex. It would advantageous to have a delivery system in which 1-MCP is incorporated into packaging materials which often surround plants or plant parts and in which 1-MCP is released without the need for adding water.
We have surprisingly found that the low concentrations of cyclopropenes needed to treat fruits, vegetables, and flowers (xe2x80x9cproducexe2x80x9d) can be released from packaging materials which incorporate the cyclopropene. The cyclopropene can be incorporated directly into many types of packaging materials or it can first be encapsulated into a molecular encapsulation agent which is then subsequently incorporated into packaging materials. We have found that moisture from humid air surrounding produce is often sufficient to release the amounts of cyclopropene required for effective treatment of the produce. In one form of the invention the powdered complex is prepared as part of the film or container. The powder can be compounded within, or laminated between, different thermoplastic packaging plastics such as polyethylene, ethyl vinylacetate, polyvinyl alcohol or with rigid plastics such as polystyrene, polycarbonate, and polymethyl methacrylate. In addition, it can be incorporated into various waxes and coated papers and cardboard or it can be incorporated into an adhesive component of packaging materials.
The present invention is, therefore, a composition comprising
a) a compound of the formula: 
xe2x80x83wherein:
1) each R1, R2, R3, and R4 is independently a group of the formula:
xe2x80x94(L)nxe2x80x94Z 
xe2x80x83wherein:
i) n is an integer from 0 to 12;
ii) each L is independently selected from a member of the group D, E or J wherein:
D is of the formula: 
E is of the formula: 
J is of the formula: 
wherein:
A) each X and Y is independently a group of the formula:
xe2x80x94(L)mxe2x80x94Z; 
xe2x80x83and
B) m is an integer from 0 to 8; and
C) no more than two E groups are adjacent to each other and no J groups are adjacent to each other;
iii) each Z is independently selected from:
A) hydrogen, halo, cyano, nitro, nitroso, azido, chlorate, bromate, iodate, isocyanato, isocyanido, isothiocyanato, pentafluorothio, or
B) a group G, wherein G is an unsubstituted or substituted; unsaturated, partially saturated, or saturated; monocyclic, bicyclic, tricyclic, or fused; carbocyclic or heterocyclic ring system wherein;
1) when the ring system contains a 3 or 4 membered heterocyclic ring, the heterocyclic ring contains 1 heteroatom;
2) when the ring system contains a 5, or more, membered heterocyclic ring or a polycyclic heterocyclic ring, the heterocyclic or polycyclic heterocyclic ring contains from 1 to 4 heteroatoms;
3) each heteroatom is independently selected from N, O, and S;
4) the number of substituents is from 0 to 5 and each substituent is independently selected from X;
2) the total number of non-hydrogen atoms in each compound is 50 or less; and
xe2x80x83its enantiomers, stereoisomers, salts, and mixtures thereof;
b) a packaging material.
For the purposes of this invention, in the structural representations of the various L groups each open bond indicates a bond to another L group, a Z group, or the cyclopropene moiety. For example, the structural representation 
indicates an oxygen atom with bonds to two other atoms; it does not represent a dimethyl ether moiety.
Another embodiment of this invention is a method to inhibit an ethylene response in a plant comprising the step of enclosing the plant in packaging which incorporates the composition of this invention.
A further embodiment is a method to prolong the life of a plant comprising the step of enclosing the plant in packaging which incorporates the composition of this invention.
Another embodiment of this invention is a method to deliver a cyclopropene compound to a plant to inhibit an ethylene response in the plant comprising the step of enclosing the plant in the composition of this invention.
As used herein, the term xe2x80x9chaloxe2x80x9d means fluorine, chlorine, bromine, and iodine.
Preferably, the number of non-hydrogen atoms in each compound is less than 25. More preferably, the number of non-hydrogen atoms in each compound is less than 20. Even more preferably, the number of non-hydrogen atoms in each compound is less than 13. Most preferably, the number of non-hydrogen atoms in the compound is less than 7.
Preferably, two of R1, R2, R3, and R4 are hydrogen. More preferably, R1 and R2 are hydrogen or R3 and R4 are hydrogen. Even more preferably, R2, R3, and R4 are hydrogen or R1, R2, and R4 are hydrogen. Most preferably, R2, R3, and R4 are hydrogen.
Preferably, R1 is (C1-C10) alkyl and R2, R3, and R4 are hydrogen. More preferably, R1 is (C1-C8) alkyl and R2, R3, and R4 are hydrogen. Even more preferably R1 is (C1-C4) alkyl and R2, R3, and R4 are hydrogen. Most preferably, R1 is methyl and R2, R3, and R4 are hydrogen.
Typical R1, R2, R3, and R4 groups include, for example: alkenyl, alkyl, alkynyl, acetylaminoalkenyl, acetylaminoalkyl, acetylaminoalkynyl, alkenoxy, alkoxy, alkynoxy, alkoxyalkoxyalkyl, alkoxyalkenyl, alkoxyalkyl, alkoxyalkynyl, alkoxycarbonylalkenyl, alkoxycarbonylalkyl, alkoxycarbonylalkynyl, alkylcarbonyl, alkylcarbonyloxyalkyl, alkyl(alkoxyimino)alkyl, carboxyalkenyl, carboxyalkyl, carboxyalkynyl, dialkylamino, haloalkoxyalkenyl, haloalkoxyalkyl, haloalkoxyalkynyl, haloalkenyl, haloalkyl, haloalkynyl, hydroxyalkenyl, hydroxyalkyl, hydroxyalkynyl, trialkylsilylalkenyl, trialkylsilylalkyl, trialkylsilylalkynyl, dialkylphosphonato, dialkylphosphato, dialkylthiophosphato, dialkylaminoalkyl, alkylsulfonylalkyl, alkylthlioalkenyl, alkylthioalkyl, alkylthioalkynyl, dialkylaminosulfonyl, haloalkylthioalkenyl, haloalkylthioalkyl, haloalkylthioalkynyl, alkoxycarbonyloxy; cycloalkenyl, cycloalkyl, cycloalkynyl, acetylaminocycloalkenyl, acetylaminocycloalkyl, acetylaminocycloalkynyl, cycloalkenoxy, cycloalkoxy, cycloalkynoxy, alkoxyalkoxycycloalkyl, alkoxycycloalkenyl, alkoxycycloalkyl, alkoxycycloalkynyl, alkoxycarbonylcycloalkenyl, alkoxycarbonylcycloalkyl, alkoxycarbonylcycloalkynyl, cycloalkylcarbonyl, alkylcarbonyloxycycloalkyl, carboxycycloalkenyl, carboxycycloalkyl, carboxycycloalkynyl, dicycloalkylamino, halocycloalkoxycycloalkenyl, halocycloalkoxycycloalkyl, halocycloalkoxycycloalkynyl, halocycloalkenyl, halocycloalkyl, halocycloalkynyl, hydroxycycloalkenyl, hydroxycycloalkyl, hydroxycycloalkynyl, trialkylsilylcycloalkenyl, trialkylsilylcycloalkyl, trialkylsilylcycloalkynyl, dialkylaminocycloalkyl, alkylsulfonylcycloalkyl, cycloalkylcarbonyloxyalkyl, cycloalkylsulfonylalkyl, alkylthiocycloalkenyl, alkylthiocycloalkyl, alkylthiocycloalkynyl, dicycloalkylaminosulfonyl, haloalkylthiocycloalkenyl, haloalkylthiocycloalkyl, haloalkylthiocycloalkynyl; aryl, alkenylaryl, alkylaryl, alkynylaryl, acetylaminoaryl, aryloxy, alkoxyalkoxyaryl, alkoxyaryl, alkoxycarbonylaryl, arylcarbonyl, alkylcarbonyloxyaryl, carboxyaryl, diarylamino, haloalkoxyaryl, haloaryl, hydroxyaryl, trialkylsilylaryl, dialkylaminoaryl, alkylsulfonylaryl, arylsulfonylalkyl, alkylthioaryl, arylthioalkyl, diarylaminosulfonyl, haloalkylthioaryl; heteroaryl, alkenylheteroaryl, alkylheteroaryl, alkynylheteroaryl, acetylaminoheteroaryl, heteroaryloxy, alkoxyalkoxyheteroaryl, alkoxyheteroaryl, alkoxycarbonylheteroaryl, heteroarylcarbonyl, alkylcarbonyloxyheteroaryl, carboxyheteroaryl, diheteroarylamino, haloalkoxyheteroaryl, haloheteroaryl, hydroxyheteroaryl, trialkylsilylheteroaryl, dialkylaminoheteroaryl, alkylsulfonylheteroaryl, heteroarylsulfonylalkyl, alkylthioheteroaryl, heteroarylthioalkyl, diheteroarylaminosulfonyl, haloalkylthioheteroaryl; heterocyclyl, alkenylheteroycycyl, alkylheteroycycyl, alkynylheteroycycyl, acetylaminoheterocyclyl, heterocyclyloxy, alkoxyalkoxyheterocyclo, alkoxyheterocyclyl, alkoxycarbonylheterocyclyl, heterocyclylcarbonyl, alkylcarbonyloxyheterocyclyl, carboxyheterocyclyl, diheterocyclylamino, haloalkoxyheterocyclyl, haloheterocyclyl, hydroxyheterocyclyl, trialkylsilylheterocyclyl, dialkylaminoheterocyclyl, alkylsulfonylheterocyclyl, alkylthioheterocyclyl, heterocyclylthioalkyl, diheterocyclylaminosulfonyl, haloalkyllthioheterocyclyl; hydrogen, fluoro, chloro, bromo, iodo, cyano, nitro, nitroso, azido, chlorato, bromato, iodato, isocyanato, isocyanido, isothiocyanato, pentafluorothio; acetoxy, carboethoxy, cyanato, nitrato, nitrito, perchlorato, allenyl; butylmercapto, diethylphosphonato, dimethylphenylsilyl, isoquinolyl, mercapto, naphthyl, phenoxy, phenyl, piperidino, pyridyl, quinolyl, triethylsilyl, trimethylsilyl; and substituted analogs thereof.
Typical G groups include, for example: saturated or unsaturated cycloalkyl, bicyclic, tricyclic, polycyclic, saturated or unsaturated heterocyclic, unsubstituted or substituted phenyl, naphthyl, or heteroaryl ring systems such as, for example, cyclopropyl, cyclobutyl, cyclopent-3-en-1-yl, 3-methoxycyclohexan-1-yl, phenyl, 4-chlorophenyl, 4-fluorophenyl, 4-bromophenyl, 3-nitrophenyl, 2-methoxyphenyl, 2-methylphenyl, 3-methyphenyl, 4-methylphenyl, 4-ethylphenyl, 2-methyl-3-methoxyphenyl, 2,4-dibromophenyl, 3,5-difluorophenyl, 3,5-dimethylphenyl, 2,4,6-trichlorophenyl, 4-methoxyphenyl, naphthyl, 2-chloronaphthyl, 2,4-dimethoxyphenyl, 4-(trifluoromethyl)phenyl, 2-iodo-4-methylphenyl, pyridin-2-yl, pyridin-3-yl, pyridin-4-yl, pyrazinyl, pyrimidin-2-yl, pyrimidin-4-yl, pyrimidin-5-yl, pyridazinyl, triazol-1-yl, imidazol-1-yl, thiophen-2-yl, thiophen-3-yl, furan-2-yl, furan-3-yl, pyrrolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, oxadiazolyl, thiadiazolyl, quinolyl, isoquinolyl, tetrahydrofuryl, pyrrolidinyl, piperidinyl, tetrahydropyranyl, morpholinyl, piperazinyl, dioxolanyl, dioxanyl, indolinyl and 5-methyl-6-chromanyl, adamantyl, norbornyl, and their substituted analogs such as, for example: 3-butyl-pyridin-2-yl, 4-bromo-pyridin-2-yl, 5-carboethoxy-pyridin-2-yl, 6-methoxyethoxy-pyridin-2-yl,
The term xe2x80x9cpackaging materialxe2x80x9d is used in a generic sense herein to include all components of packaging in which fruits, vegetables, or ornamental plants may be contained such as, for example, packaging films; a container such as, for example, a cardboard, plastic, or wooden box or paper bag; or wax or film coating on the plant or the container. Encapsulated cyclopropenes can be compounded within, or laminated between, different thermoplastic packaging plastics such as polyethylene, ethyl vinylacetate, polyvinyl alcohol or with rigid plastics such as polystyrene, polycarbonate, and polymethyl methacrylate. In addition, the cyclopropene, either free or encapsulated, can be incorporated into various waxes, coated papers, and cardboard or it can be incorporated into an adhesive component of packaging materials or incorporated into package labels.
The amount of cyclopropene to be incorporated into the packaging material will vary depending upon particular cyclopropene, the type and amount of packaging material used, the composition of the packaging material, the quantity of plant material to be enclosed, and the volume to be enclosed. Generally, in order to obtain a concentration of cyclopropene in the enclosed volume of from about 1 part per billion (xe2x80x9cppbxe2x80x9d) to 1000 parts per million (xe2x80x9cppmxe2x80x9d) a concentration of the cyclopropene in the packaging material of from 0.0001 to 100 milligrams (xe2x80x9cmgxe2x80x9d) per square meter of surface area of the packaging material is required. Preferably, the concentration of cyclopropene will be from 0.001 to 10 mg per square meter. More preferably from 0.01 to 1 mg per square meter. This corresponds, respectively, to approximately 10 ppb-100 ppm and 100 ppb to 10 ppm of cyclopropene released into the volume packaged by each square meter of packaging material.
The term xe2x80x9cenclosingxe2x80x9d means to surround, close in, or confine the plant. In the general sense it means to place the plant in close contact with the packaging material so that the plant can be shipped or stored.
Because cyclopropenes are known to release from packaging materials by diffusion or by displacement by water, particularly when the cyclopropene is encapsulated in a molecular encapsulation agent, this invention also contemplates articles in which the composition of this invention is enclosed in a container which is impermeable to the cyclopropene gas, or water, or both. Such an article of manufacture includes, for example, labels in which the cyclopropene is incorporated into the label material itself or the label adhesive.
The cyclopropene can be incorporated directly into many types of packaging materials or it can first be encapsulated into a molecular encapsulation agent which is then subsequently incorporated into packaging materials. Preferred encapsulating agents include cyclodextrins, crown ethers, polyoxyalkylenes, polysiloxanes, and zeolites. More preferred encapsulating agents include xcex1-cyclodextrin, xcex2-cyclodextrin, and xcex3-cyclodextrin. The most preferred encapsulating agent, particularly when the cyclopropene is 1-methylcyclopropene, is alpha-cyclodextrin. The most preferred encapsulating agent will vary depending upon the size of the R substituents. However, as one skilled in the art will appreciate, any cyclodextrin or mixture of cyclodextrins, cyclodextrin polymers as well as modified cyclodextrins can also be utilized pursuant to the present invention. Cyclodextrins are available from Wacker Biochem Inc., Adrian, Mich. or Cerestar USA, Hammond, Ind., as well as other vendors.
The term xe2x80x9cplantxe2x80x9d is used in a generic sense herein, and includes woody-stemmed plants such as trees and shrubs. Plants to be packaged as described herein include whole plants and any portions thereof, such as harvested field crops, potted plants, cut flowers (stems and flowers), other ornamental plants, seeds, dormant seedlings, and harvested fruits and vegetables.
The present invention can be employed to modify a variety of different ethylene responses. Ethylene responses may be initiated by either exogenous or endogenous sources of ethylene. Ethylene responses include, for example, the ripening and/or senescence of flowers, fruits and vegetables, abscission of foliage, flowers and fruit, the shortening of life of ornamentals such as potted plants, cut flowers, shrubbery, seeds, and dormant seedlings. Additional ethylene responses or ethylene-type responses that may be inhibited by the composition of the present invention include, for example, auxin activity, inhibition of terminal growth, control of apical dominance, increase in branching, increase in tillering, changing biochemical compositions of plants (such as increasing leaf area relative to stem area), abortion or inhibition of flowering and seed development, stimulation of seed germination and breaking of dormancy, and hormone or epinasty effects.
Methods according to embodiments of the present invention inhibit the ripening and/or senescence of vegetables. As used herein, xe2x80x9cvegetable ripeningxe2x80x9d includes the ripening of the vegetable after having been picked from the vegetable-bearing plant. Vegetables which may be treated by the composition of the present invention to inhibit ripening and/or senescence include leafy green vegetables such as lettuce (e.g., Lactuea sativa), spinach (Spinaca oleracea), and cabbage (Brassica oleracea), various roots, such as potatoes (Solanum tuberosum) and carrots (Daucus), bulbs, such as onions (Allium sp.), herbs, such as basil (Ocimum basilicum), oregano (Origanum vulgare), dill (Anethum graveolens), as well as soybean (Glycine max), lima beans (Phaseolus linensis), peas (Lathyrus spp.), corn (Zea mays), broccoli (Brassica oleracea italica), cauliflower (Brassica oleracea botrytis), and asparagus (Asparagus officinalis).
Methods according to embodiments of the present invention inhibit the ripening of fruits. As used herein, xe2x80x9cfruit ripeningxe2x80x9d includes the ripening of fruit after having been picked from the fruit-bearing plant. Fruits which may be treated by the method of the present invention to inhibit ripening include tomatoes (Lycopersicon esculentum), apples (Malus domestica), bananas (Musa sapientum), pears (Pyrus comrnunis), papaya (Carica papaya), mangoes (Mangifera indica), peaches (Prunus persica), apricots (Prunus armeniaca), nectarines (Prunus persica nectectarina), oranges (Citrus sp.), lemons (Citrus limonia), limes (Citrus aurantifolia), grapefruit (Citrus paradisi), tangerines (Citrus nobilis deliciosa), kiwi (Actinidia chinenus), melons such as cantaloupe (C. cantalupensis) and musk melon (C. melo), pineapple (Aranas comosus), persimmon (Diospyros sp.), various small fruits including berries such as strawberries (Fragaria), blueberries (Vaccinium sp.) and raspberries (e.g., Rubus ursinus), green beans (Phaseolus vulgaris), members of the genus Cucumis such as cucumber (C. sativus), and avocados (Persea americana).
Ornamental plants which may be treated by the composition of the present invention to inhibit senescence and/or to prolong flower life and appearance (e.g., delay wilting), include potted ornamentals, and cut flowers. Potted ornamentals and cut flowers which may be treated with the present invention include azalea (Rhododendron spp.), hydrangea (Macrophylla hydrangea), hybiscus (Hibiscus rosasanensis), snapdragons (Antirrhinum sp.), poinsettia (Euphorbia pulcherima), cactus (e.g. Cactaceae schlumbergera truncata), begonias (Begonia sp.), roses (Rosa spp.), tulips (Tulipa sp.), daffodils (Narcissus spp.), petunias (Petunia hybrida), carnation (Dianthus caryophyllus), lily (e.g., Lilium sp.), gladiolus (Gladiolus sp.), alstroemeria (Alstoemeria brasiliensis), anemone (e.g., Anemone blanda), columbine (Aquilegia sp.), aralia (e.g., Aralia chinensis), aster (e.g., Aster carolinianus), bougainvillea (Bougainvillea sp.), camellia (Camellia sp.), bellflower (Campanula sp.), cockscomb (celosia sp.), falsecypress (Chamaecyparis sp.), chrysanthemum (Chrysanthemum sp.), clematis (Clematis sp.), cyclamen (Cyclamen sp.), freesia (e.g., Freesia refracta), and orchids of the family Orchidaceae.
Plants which may be treated by the method of the present invention to inhibit abscission of foliage, flowers and fruit include cotton (Gossypium spp.), apples, pears, cherries (Prunus avium), pecans (Carva illinoensis), grapes (Vitis vinifera), olives (e.g. Vitis vinifera and Olea europaea), coffee (Coffea arabica), snapbeans (Phaseolus vulgaris), and weeping fig (ficus benjamina), as well as dormant seedlings such as various fruit trees including apple, ornamental plants, shrubbery, and tree seedlings. In addition, shrubbery which may be treated according to the present invention to inhibit abscission of foliage include privet (Ligustrum sp.), photinea (Photinia sp.), holly (Ilex sp.), ferns of the family Polypodiaceae, schefflera (Schefflera sp.), aglaonema (Aglaonema sp.), cotoneaster (Cotoneaster sp.), barberry (Berberis sp.), waxmyrtle (Myrica sp.), abelia (Abelia sp.), acacia (Acacia sp.) and bromeliades of the family Bromeliaceae.
As used herein, all percentages are percent by weight and all parts are parts by weight, unless otherwise specified, and are inclusive and combinable. All ratios are by weight and all ratio ranges are inclusive and combinable. All molar ranges are inclusive and combinable.
Many of the cyclopropenes applicable to this invention are known materials prepared using the processes disclosed in U.S. Pat. Nos. 5,518,988 and 6,017,849. The cyclopropene/molecular encapsulation agent complexes of the present invention are prepared by contacting the cyclopropene with a solution or slurry of the molecular encapsulation agent and then isolating the complex, again using general processes disclosed in U.S. Pat. No. 6,017,849. In the case of 1-methylcyclopropene, the gas is bubbled through a solution of xcex1-cyclodextrin in water from which the complex first precipitates and is then isolated by filtration.
The compounds of this invention can be prepared by a number of methods. For general references see Closs, G. L. Advan. Alicyclic Chem. 1966, 1, 53-127 and Al Dulayymi, A. R.; Al Dulayymi, J. R; Baird, M. S.; and Koza, G. Russian Journal of Organic Chemistry 1997, 33, 798-816.
The reaction of a bromo-olefin with dibromocarbene gives a tribromocyclopropane, which can be converted to the cyclopropene with methyllithium or other organolithium compounds as shown. (see Baird, M. S.; Hussain, H. H.; Nethercott, W J. Chem. Soc. Perkin Trans. 1, 1986, 1845-1854 and Baird, M. S.; Fitton, H. L.; Clegg, W; McCamley, A. J. Chem. Soc. Perkin Trans. 1, 1993, 321-326). If one equivalent of methyllithium or other alkyllithium is used, the mono-brominated cyclopropene is obtained. With 2 or more equivalents of the alkyllithium, the lithiated cyclopropene is formed. This can be quenched with water to give the cyclopropenes shown (Exe2x95x90H). Alternatively, the cyclopropenyllithium can be reacted with electrophiles to give derivatived cyclopropenes. Examples of such electrophiles include alkylating agents, trisubstituted chlorosilanes, borates, dialkyl or diaryl disulfides, ketones, aldehydes, esters, amides and nitrites. 
The bromo-olefins can be prepared by standard methods. Chloro-olefins can be used in place of bromo-olefins.
The tribrominated cyclopropanes can also be converted to mono-brominated cyclopropanes with reducing agents such as diethylphosphite. Other reducing agents could be used. 
A 1,1-disubstituted olefin can also react with dibromocarbene to give a dibrominated intermediate. This can be reduced with zinc to the mono-brominated cyclopropane. Elimination of the bromide with base gives the cyclopropene (reference Binger, P. Synthesis 1974, 190). 
Cyclopropene can be deprotonated with a strong base such as sodium amide in liquid ammonia and reacted with an alkyl halide or other electrophiles to give a substituted cyclopropene (reference: Schipperijn, A. J.; Smael, P.,; Recl. Trav. Chin. Pays-Bas, 1973, 92, 1159). Substituted cyclopropenes can be deprotonated with alkyllithium reagents and reacted with electrophiles. 
Tribromocyclopropanes or cyclopropenes containing an alcohol can be converted to a good leaving group such as a sulfonate derivative. The leaving group can be displaced with nucleophiles to give other substituted cyclopropenes. 
A 1-trialkylsilyl-2-hydroxycyclopropane, generated from vinyltrialkylsilane, can serve as a precursor to a cyclopropene (Mizojiri, R.; Urabe, H.; Sato, F. J. Org Chem. 2000, 65, 6217). 
1-Trialkylsilyl-2-halocyclopropanes also undergo a fluoride catalyzed elimination to give cyclopropenes (Billups, W. E.; Lee, G-A; Arney, B. E.; Whitmire, K. H. J. Am. Chem. Soc., 1991, 113, 7980. and Banwell, M. G.; Corbett, M.; Gulbis, J.; Mackay, M. F.; Reum, M. E. J. Chem. Soc. Perkin Trans. 1, 1993, 945).
The addition of a diazo compound to an acetylene is another method that can be used for the synthesis of cyclopropenes (Mueller, P.; Cranisher, C; Helv. Chim. Acta 1993, 76, 521). 
The esters can be hydrolyzed to the carboxylic acid.
Similarly, dihalocarbenes can be added to acetylenes to give 1-alkyl-3,3-dihalocyclopropenes (Bessard, Y.; Schlosser, M.; Tetrahedron, 1991, 47, 7323).
Compounds of this invention can also be obtained from a malonate derivative as shown. 
Other methods for making cyclopropenes can be found in the following references: Duerr, H., Angew. Chem. 1967, 24, 1104; Closs et al., J. Am. Chem. 1963, 85, 3796; Baird, M. S.; Dale, C. M.; Al Dulayymi, J. R. J. Chem. Soc. Perkin Trains. 1, 1993, 1373-1374; Koster, R. et al., Liebigs Annalen Chem. 1973, 1219-1235; Closs, G. L.; Closs, L. E., J. Am. Chem. Soc., 1961, 83, 1003-1004; Stoll, A. T.; Negishi, E., Tetrahedron Lett. 1985, 26, 5671-5674.